This invention relates generally to a method and system for reducing artifacts in an image and more particularly to a method and system using an image space compensation scheme for reducing artifacts in an X-ray image generated by a Computed Tomography (CT) imaging system.
In CT imaging systems, an x-ray source projects a fan-shaped beam that is collimated to lie within an X-Y plane, generally referred to as an xe2x80x9cimaging planexe2x80x9d, of a Cartesian coordinate system toward an array of radiation detectors, wherein each radiation detector includes a detector element disposed within the CT system so as to receive this fan-shaped beam. An object, such as a patient, is disposed between the x-ray source and the radiation detector array so as to lie within the imaging plane and so as to be subjected to the x-ray beam, which passes through the object. As the x-ray beam passes through the object, the x-ray beam becomes attenuated before impinging upon the array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is responsive to the attenuation of the x-ray beam by the object, wherein each detector element produces a separate electrical signal responsive to the beam intensity at the detector element location. These electrical signals are referred to as x-ray attenuation measurements or x-ray images.
Moreover, the x-ray source and the detector array may be rotated, with a gantry within the imaging plane, around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements, i.e., projection data, from the detector array at one gantry angle is referred to as a xe2x80x9cviewxe2x80x9d. A xe2x80x9cscanxe2x80x9d of the object comprises a set of views made at different gantry angles during one revolution of the x-ray source and the detector array. In an axial scan, the projection data is processed so as to construct an image that corresponds to a two-dimensional slice taken through the object. In CT systems that employ a single detector array, the slice thickness is controlled and determined by the width of the collimator, while in CT systems that employ a multiple detector array, the slice thickness is controlled and determined by summing the contributions of a plurality of detector sub-units and by physically moving the collimator to the outer edges of each slice.
With the introduction of multi-slice computed tomography (CT), nearly isotropic spatial resolution may be obtained using helical scans. In order to reduce the number of images necessary for each study, more and more radiologists utilize 3-D visualization tools to perform diagnosis. One of the more popular visualization tools employs a technique known as maximum intensity projection (MIP) processing.
In MIP processing the direction of an imaginary ray forward projection is determined and a maximum pixel value along each forward projection ray is identified. The projection value for each projection ray is then assigned to this maximum pixel value, resulting in the production of 2-D projection data from a 3-D image volume. In addition, a similar but slightly different visualization technique is called volume rendering (VR). In VR, an imaginary ray forward projection is also produce, but unlike the MIP process the projection value is determined based on the integrated opacity along the projection ray path. The opacity is obtained based on a mapping function that maps the image intensity to certain opacity values.
However, because of the interaction between the helical weighting and the scaling in the fan-beam back-projection process, the noise in the reconstructed image is both non-uniform and non-stationary and thus no longer homogenous. In addition, because the noise variation follows the x-ray tube position a periodic intensity modulation in the MIP image, known as the Venetian blind artifact or zebra artifact, is created. Thus, as a result of the inhomogeneous nature of the noise distribution in 3D or MIP images bias, in the form of bright and dark bands or spiral pattern artifacts, is produced. For certain weighting functions, the noise difference can be more than a factor of two even for the reconstruction of a homogeneous object.
Unfortunately, two obstacles currently exist with present methods of removing or reducing these artifacts from reconstructed images. First, these methods require a great deal of time and processing power in order to reconstruct the image. Second, these methods are unable to handle images having large amounts of artifacts. Therefore, there is a need for an algorithm that facilitates the reduction of artifacts, wherein the algorithm does not significantly increase the image reconstruction processing time.
The above discussed and other drawbacks and deficiencies are overcome or alleviated by a method for reducing artifacts in an x-ray image generated by a computed tomography imaging system using an image space compensation scheme comprising: obtaining reconstructed image data generated using an image reconstruction algorithm; determining a noise variation characteristic for the reconstruction algorithm; filtering the reconstructed image data so as to create smoothed image data and processing the smoothed image data and the reconstructed image data so as to create corrected image data.
A medium encoded with a machine-readable computer program code for reducing artifacts in an x-ray image generated by a computed tomography imaging system using an image space compensation scheme, the medium including instructions for causing a controller to implement a method comprising: obtaining reconstructed image data generated using an image reconstruction algorithm; determining a noise variation characteristic for the reconstruction algorithm; filtering the reconstructed image data so as to create smoothed image data; and processing the smoothed image data and the reconstructed image data so as to create corrected image data.
A method for reducing artifacts in an image comprising: obtaining an imaging system and an object to be scanned; operating the imaging system so as to create projection data responsive to the object; examining the projection data so as to determine if the projection data should be processed; and processing the projection data using an image space compensation scheme wherein the compensation scheme, obtains reconstructed image data generated using an image reconstruction algorithm; determines a noise variation characteristic for the reconstruction algorithm; filters the reconstructed image data so as to create smoothed image data; and processes the smoothed image data and the reconstructed image data so as to create corrected image data.
A system for reducing artifacts in an x-ray image comprising: a gantry having an x-ray source and a radiation detector array, wherein the gantry defines an object cavity and wherein the x-ray source and the radiation detector array are rotatingly associated with the gantry so as to be separated by the object cavity; a object support structure movingly associated with the gantry so as to allow communication with the object cavity; and a processing device having an image space compensation scheme, wherein the compensation scheme, obtains reconstructed image data generated using an image reconstruction algorithm; determines a noise variation characteristic for the reconstruction algorithm; filters the reconstructed image data so as to create smoothed image data; and processes the smoothed image data and the reconstructed image data so as to create corrected image data.
A system for reducing artifacts in an image using an image space compensation scheme comprising: an imaging system; an object disposed so as to be communicated with the imaging system, wherein the imaging system generates projection data responsive to the object; and a processing device, wherein the processing device, obtains reconstructed image data generated using an image reconstruction algorithm; determines a noise variation characteristic for the reconstruction algorithm; filters the reconstructed image data so as to create smoothed image data; and processes the smoothed image data and the reconstructed image data so as to create corrected image data.